Observations of ultraviolet-bright stars in globular clusters with the Hopkins Ultraviolet Telescope

Abstract

view Abstract Citations (14) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Observations of Ultraviolet-Bright Stars in Globular Clusters With The Hopkins Ultraviolet Telescope Dixon, W. Van Dyke ; Davidsen, Arthur F. ; Ferguson, Henry C. Abstract Two UV-bright stars in globular clusters, UV5 in NGC 1851 and vZ 1128 in M3, were observed with the Hopkins Ultraviolet Telescope (HUT) during the Astro-1 space shuttle mission in 1990 December. The stars' spectra show weak absorption features and no significant emission features other than well known geocoronal lines. Detailed fitting of Kurucz (1991) stellar atmosphere models using a chi2 minimization technique indicates Teff = 16 000 K, log g = 2.5, and abundance (-1.0) (logarithm of abundance of elements heavier than helium relative to solar) for UV5, and Teff = 35 000 K, log g = 4.0, and abundance (-3.5) for vZ 1128. The Kurucz model which best fits vZ 1128 overpredicts the flux in the region below approximately 1000 A, an effect seen in previous models of O-type stars. Our results are robust (to within approximately 1000 K) with respect to uncertainties in interstellar reddening and atomic and molecular hydrogen column densities. We do not see significant molecular hydrogen absorption, which might have indicated material in a circumstellar shell, in either star's spectrum. We estimate the stellar luminosities to be log L/solar luminosity = 3.33 +/- 0.15 for UV5 and log L/solar luminosity = 3.21 +/- 0.12 for vZ 1128. These atmospheric parameters place both stars on the Schoenberner (post-AGB) tracks, though the stellar masses derived from the best-fitting Kurucz models are somewhat less than those predicted by the Schoenberner models. Examination of individual absorption line strengths reveals no significant abundance anomalies in either star. Publication: The Astronomical Journal Pub Date: April 1994 DOI: 10.1086/116952 Bibcode: 1994AJ....107.1388D Keywords: Absorption Spectra; Airglow; Data Reduction; Galactic Halos; Globular Clusters; Stellar Evolution; Stellar Luminosity; Stellar Mass; Ultraviolet Spectra; White Dwarf Stars; Interstellar Extinction; Interstellar Matter; Stellar Models; Ultraviolet Radiation; Ultraviolet Telescopes; Astronomy; GLOBULAR CLUSTERS: GENERAL; ULTRAVIOLET: STARS full text sources ADS | data products SIMBAD (4) MAST (2) INES (1)